It is well known that vacuum cleaner bags or containers become filled upon use and require replacement from time to time. In order to increase the efficiency of the vacuum cleaner it is disirable to know when the bag needs replacing. Furthermore, damage to the vacuum cleaner motor is prevented inasmuch as the motors are generally dependent upon the air flow present in the vacuum cleaner housing for cooling.
In order to alert the vacuum cleaner user to the fact that the bag requires replacement, signal devices have been previously used which are dependent upon the pressure differences prevailing between the inlet and the outlet of the dust container. This pressure difference is used to move a member, such as a piston in a cylinder, that is visible from the exterior of the apparatus. Thus, when the dust bag is filled the piston has been moved to such a position indicating that the vacuum cleaner bag replacement is necessary.
The above-described construction has a serious drawback in that the interior of the signalling devices employed become contaminated by a reason of the air-borne particles passing therethrough. This situation occurs since there is a higher absolute pressure inside the dust container and in spite of the use of seals the dust particles are capable of finding their way through the space between the outer surface of the piston and the inner surface of the cylinder to the other end of the piston where a lower absolute pressure is in existence. It will be evident that some dirt particles may adhere in the confined space between the piston and cylinder and thereby jeopardize the correct operation of the signal device by failing to indicate, at the proper time, the need for a bag replacement.
In previously known signal devices for vacuum cleaners a filter is provided in the channel connecting the interior of the dust container to the signal device. However, a serious drawback has arisen since the filter must be changed at regular intervals in order to ensure a reliable indication or simply the general operation of the signal device.
It is an object of the present invention to overcome the above-mentioned serious disadvantage and to provide a construction that prevents dust and dirt particles present in the interior of the dust container from penetrating into the components of the signalling device by eliminating a filter device and utilizing a communicating means in the attachment plate of a vacuum cleaner bag in which a first air channel is formed which communicates the dust container to the signalling device with a part of the dust container functioning as an air pervious member in the air flow path.